Field of the Invention
The present invention relates to a fuel injection valve controller apparatus for use in a combustion engine and particularly, to a fuel injection valve controller apparatus suited to steadily detect the completion of opening of the fuel injection valve or the completion of the needle valve lifting movement.
FIG. 7 is a longitudinal cross sectional view showing a conventional electromagnetic fuel injection valve (referred to as an "injection valve" hereinafter). A hollow sleeve 2 made of a magnetic material is fitted into a cylindrical housing 1 made of a similar magnetic material. The hollow sleeve 2 includes a stationary core 2a, a flange 2b, and a fuel inlet member 2c. A bobbin 3 and an electromagnetic coil 4 (referred to as a "coil" hereinafter) wound on the bobbin 3 are disposed in a space between the housing 1 and the stationary core 2a so that it surrounds the stationary core 2a. The stationary core 2a has a compression coil spring 5 therein for urging a plunger (movable core) 6, which is located opposite to one end of the hollow sleeve 2, in a direction to close the injection valve.
A valve seat 8 is provided in the tip of the housing 1, which slidably accommodates a needle valve 7 coupled to the movable core 6.
The valve seat 8 is covered with a nozzle 9 and swagelocked together with the nozzle 9 to one (front) opening end of the housing 1. The flange 2b of the hollow sleeve 2 is also swagelocked to the other or rear opening end of the housing 1. The flange 2b is fixedly joined at top with a connector 10 made of an insulating material such as resin. The connector 10 has a terminal 10a therein electrically connected to the coil 4. The fuel inlet member 2c of the hollow sleeve 2 accommodates a strainer 12 which includes a filter net 11 therein. A fuel is admitted through the hollow sleeve 2 as shown by the arrow A and flown to a space between the valve seat 8 and the needle valve 7.
In operation, energizing of the coil 4 through the terminal 10a causes the movable core 6 to be attracted toward the hollow sleeve 2 and the needle valve 7 to depart from the valve seat 8 as resisting against the yielding force of the compression coil spring 5. Accordingly, the fuel is ejected out from an injection aperture 13 provided in the front end of the valve seat 8. The energizing of the coil 4 or the injection of the fuel can be controlled depending on an operating condition of the engine.
For improving the response of the injection valve to the operating condition of the engine or making the injection valve compatible with injection of a large amount of fuel such as in a direct injection engine or a gaseous fuel internal combustion engine, it is essential to supply the coil 4 with a large quantity of electric current and thus increase the magnetic attraction of the stationary core 2a for valve opening. However, if such a higher current were fed throughout the energizing period, the temperature of the coil 4 may radically increase and extra scheme for radiating heat from relevant switching elements (or drivers) in a drive circuit for energizing the coil 4 will be needed and it will be rather difficult to realize in the industrial field.
For a countermeasure thereof, the coil current is provided of a higher intensity at the starting of valve opening and it is reduced to the level of maintaining the valve opening after completion of the valve opening (when the needle valve has been lifted up).
It is known that the coil current in the injection valve is varied depending on a change (increase) of the inductance due to the position of the movable core, that is, the coil current decreases as the needle valve is fully lifted up (as for example disclosed in Japanese Patent Publication No. SHO 62-4543). For example, a controller apparatus disclosed in Japanese Patent Laid-open Publication No. SHO 58-211538 provides detecting the completion of valve opening from a drop of the coil current corresponding to the end of lifting operation and then decreasing the coil current.
The following disadvantage exist in such a conventional controller apparatus capable of reducing the coil current, after the coil current reaches at a specific or singular point, to a minimum level enough to hold the valve opening. The conventional controller apparatus allows the specific point to be recognized by detecting a point where a variation in the coil current is shifted again from negative to positive after it has once turned from positive to negative. However, this means may find it difficult to detect the specific point in some cases. For example, the shift of the coil current from positive to negative is attenuated by change in the source voltage for supply of the coil current, change in the coil temperature, and/or change in the pressure of fuel injection and, therefore, the shift back to positive from negative will thus be recognized with much difficulty. Accordingly, the stable detection of the specific point can hardly be consistent resulting in unstable control over the coil current.